Fluid measurement, control and manipulation are very important in many applications. Direct, accurate on-line measurement of mass flow and fluid density has been made possible through the development of different types of direct mass flow meters. One simple but effective device of this kind is known as the gyroscopic mass flow meter, which takes advantage of the Coriolis force in making measurements.
Since there is but one way of generating Coriolis forces, all existing devices based on gyroscopic or Coriolis force utilize the same basic principles, but specify different means for measuring the force. A number of approaches have been taken in utilizing Coriolis forces to measure mass flow. For instance, Roth, U.S. Pat. Nos. 2,865,201, 3,276,257, and 3,312,512, disclose gyroscopic flow meters employing a full loop, which is continuously rotated (DC type) or oscillated (AC type). The first commercial Coriolis mass flowmeter was introduced in 1977 by Micro Motion Inc. (Boulder, Colo), a member of Rosemount Instrumentation and Control Group. U.S. Pat. No. 4,109,524 teaches the basic principle of this sensor and its construction. Such direct mass flow meters were the first to provide direct, accurate, on-line measurement of mass flow and fluid density. Their major advantages are direct mass flow and fluid density measurements, good accuracy, and high stability. Their major shortcomings are large size and high cost.
Developments in microfabrication techniques and silicon micromachining technology have made it possible to make precision structures for fluidic applications. Silicon as a micromechanical material has been discussed in many papers (J. B. Agnell et. al., 1983, K. E. Bean, 1978, K. E. Petersen, 1982). J. Chen and K. D. Wise have described the methods of making micromachined tubes and channels in silicon. In addition, Peter Enokssen et al. has reported bulk micromachined resonant silicon tube density sensors and mass flow sensors using optical techniques. The need remains, however, to exploit silicon microfabrication techniques to a greater extent in fabricating fluidic apparatus, including direct mass flow meters. It would be particularly advantageous to apply silicon microtubes and other technology to the development of gyroscopic mass flow meters based upon the Coriolis effect.